The present invention generally relates to a method and system for detecting dislodgment of an implanted right atrial endocardial lead. The present invention is more particularly directed to such a system and method incorporated within an implantable atrial defibrillator having, in addition to atrial fibrillation cardioversion capability, at least atrial pacing, and more particularly, atrial antitachycardia pacing capability.
Atrial fibrillation is probably the most common cardiac arrhythmia. Although it is not usually a life-threatening arrhythmia, it is associated with strokes thought to be caused by blood clots forming in areas of stagnant blood flow as a result of prolonged atrial fibrillation. In addition, patients afflicted with atrial fibrillation generally experience rapid and irregular beating of the heart and may even experience dizziness as a result of reduced cardiac output.
Atrial fibrillation occurs suddenly, and many times can only be corrected by discharging electrical energy into the atria of the heart of the patient. This treatment is preferably synchronized to a detected R wave of the heart in order to avoid shocking the atria during the T wave or vulnerable period of the heart. The amount of energy which may be required to successfully cardiovert the atria can be as low as one joule and as high as six joules. In most cases, energy of about two to four joules is required to cardiovert atrial fibrillation back to normal sinus rhythm (NSR).
Atrial tachycardia is a less common accelerated atrial arrhythmia. It is a more organized arrhythmia than atrial fibrillation characterized by a very fast and substantially constant atrial rate. Atrial tachycardia results in many of the same symptoms as atrial fibrillation. It can result in dizziness, shortness of breath and a rapid ventricular rate.
Implantable atrial defibrillators are known which detect the presence of atrial fibrillation and provide a single cardioverting pulse of electrical energy to the atria when atrial fibrillation is detected. Usually, the therapy is applied in synchrony with a detected R wave to avoid therapy application during the ventricular vulnerable period of the heart thereby preventing the induction of a lethal ventricular arrhythmia.
Antitachycardia atrial pacing is often used as a therapy for atrial tachycardia. In such therapy, the atria are paced at a rate faster than the atrial intrinsic rate for a time to terminate the atrial tachycardia. This is commonly known as overdrive pacing.
To accomplish overdrive pacing, the right atrium is commonly paced at a high rate by an implanted device. The implanted device applies pacing pulses to the right atrium with a pair of small, closely spaced, electrodes, generally referred to as a bipolar electrode pair. The electrodes are carried on an implantable endocardial lead. The lead is designed for fixation in the right atrium, either by tines or by a helical screw-in tip which can serve as one of the electrodes. Both forms of fixation are well known in the art.
One potential problem with atrial antitachycardia pacing is an inadvertent dislodgment of the right atrial endocardial lead. Should the lead become dislodged, the atrial pacing electrodes could be displaced to a position close to or within the right ventricle. High rate antitachycardia pacing intended for the right atrium with the lead in such a dislodged position could cause the ventricles to be overdrive paced. This presents the possibility of accelerating the ventricles into a dangerous and potentially life threatening arrhythmia.
Atrial antitachycardia pacing can still be a very useful therapy. A significant number of atrial fibrillation patients suffer from this arrhythmia. Hence, it would be advantageous to be able to incorporate this therapy into an implantable atrial defibrillator. By virtue of the present invention, atrial antitachycardia pacing may be incorporated within implantable devices, such as an atrial defibrillator.